The following macro will do it:
Sub CountSheets()
Dim Criterion As String
Dim Sh As Object
Dim ShCount As Integer
ShCount = 0
Criterion = InputBox("Enter name matching criterion", _
"Count of Matching Sheet Names", "CO*")
If Criterion = "" Then Exit Sub
For Each Sh In Sheets
If Sh.Name Like Criterion Then ShCount = ShCount + 1
Next Sh
MsgBox ShCount & " sheet names match criterion", vbInformation, _
"Count Sheets Results"
End Sub
This is set up to look for sheets starting with CO (the asterisk is a wildcard character matching any number of characters after CO). To match OPT simply enter OPT* when prompted for the matching criterion.
Damon